SPLongOperation usage and SPDisposeCheck

Question

I'm trying to use SPLongOperation like in the snippet below. When I run SPDisposeCheck, I get an error. So I have these questions:

1. Wouldn't the using statement call Dispose() on SPSite when execution is completed?

2. How can I give a friendly error message, regardless of the type of exception thrown during the long runnig process?

   protected void btn_click(object sender, EventArgs e)
   {
       // ..... removed for brevity
   
       SPLongOperation longOp = new SPLongOperation(this.Page);
       longOp.Begin();
   
       try     //getting error: Disposable type not disposed: Microsoft.SharePoint.SPSite
       {
           using(SPSite oSite = new SPSite(SPContext.Current.Site.Url))
           {
               using(SPWeb oWeb = oSite.OpenWeb(client))
               {
   
                   // do long running process
                   // throw new Exception("Something went wonky!");
   
               }
           }
   
           longOp.End(redirectUrl);
       }
       catch (ThreadAbortException)
       {
   
       }
       catch (Exception ex)
       {
           SPUtility.TransferToErrorPage(ex.ToString());
       }
   
   }